/*

 * jmemsys.h

 *

 * Copyright (C) 1992-1994, Thomas G. Lane.

 * This file is part of the Independent JPEG Group's software.

 * For conditions of distribution and use, see the accompanying README file.

 *

 * This include file defines the interface between the system-independent

 * and system-dependent portions of the JPEG memory manager.  No other

 * modules need include it.  (The system-independent portion is jmemmgr.c;

 * there are several different versions of the system-dependent portion.)

 *

 * This file works as-is for the system-dependent memory managers supplied

 * in the IJG distribution.  You may need to modify it if you write a

 * custom memory manager.  If system-dependent changes are needed in

 * this file, the best method is to #ifdef them based on a configuration

 * symbol supplied in jconfig.h, as we have done with USE_MSDOS_MEMMGR.

 */





/* Short forms of external names for systems with brain-damaged linkers. */



#ifdef NEED_SHORT_EXTERNAL_NAMES

#define jpeg_get_small		jGetSmall

#define jpeg_free_small		jFreeSmall

#define jpeg_get_large		jGetLarge

#define jpeg_free_large		jFreeLarge

#define jpeg_mem_available	jMemAvail

#define jpeg_open_backing_store	jOpenBackStore

#define jpeg_mem_init		jMemInit

#define jpeg_mem_term		jMemTerm

#endif /* NEED_SHORT_EXTERNAL_NAMES */





/*

 * These two functions are used to allocate and release small chunks of

 * memory.  (Typically the total amount requested through jpeg_get_small is

 * no more than 20K or so; this will be requested in chunks of a few K each.)

 * Behavior should be the same as for the standard library functions malloc

 * and free; in particular, jpeg_get_small must return NULL on failure.

 * On most systems, these ARE malloc and free.  jpeg_free_small is passed the

 * size of the object being freed, just in case it's needed.

 * On an 80x86 machine using small-data memory model, these manage near heap.

 */



EXTERN void * jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject));

EXTERN void jpeg_free_small JPP((j_common_ptr cinfo, void * object,

				 size_t sizeofobject));



/*

 * These two functions are used to allocate and release large chunks of

 * memory (up to the total free space designated by jpeg_mem_available).

 * The interface is the same as above, except that on an 80x86 machine,

 * far pointers are used.  On most other machines these are identical to

 * the jpeg_get/free_small routines; but we keep them separate anyway,

 * in case a different allocation strategy is desirable for large chunks.

 */



EXTERN void FAR * jpeg_get_large JPP((j_common_ptr cinfo,size_t sizeofobject));

EXTERN void jpeg_free_large JPP((j_common_ptr cinfo, void FAR * object,

				 size_t sizeofobject));



/*

 * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may

 * be requested in a single call to jpeg_get_large (and jpeg_get_small for that

 * matter, but that case should never come into play).  This macro is needed

 * to model the 64Kb-segment-size limit of far addressing on 80x86 machines.

 * On those machines, we expect that jconfig.h will provide a proper value.

 * On machines with 32-bit flat address spaces, any large constant may be used.

 *

 * NB: jmemmgr.c expects that MAX_ALLOC_CHUNK will be representable as type

 * size_t and will be a multiple of sizeof(align_type).

 */



#ifndef MAX_ALLOC_CHUNK		/* may be overridden in jconfig.h */

#define MAX_ALLOC_CHUNK  1000000000L

#endif



/*

 * This routine computes the total space still available for allocation by

 * jpeg_get_large.  If more space than this is needed, backing store will be

 * used.  NOTE: any memory already allocated must not be counted.

 *

 * There is a minimum space requirement, corresponding to the minimum

 * feasible buffer sizes; jmemmgr.c will request that much space even if

 * jpeg_mem_available returns zero.  The maximum space needed, enough to hold

 * all working storage in memory, is also passed in case it is useful.

 * Finally, the total space already allocated is passed.  If no better

 * method is available, cinfo->mem->max_memory_to_use - already_allocated

 * is often a suitable calculation.

 *

 * It is OK for jpeg_mem_available to underestimate the space available

 * (that'll just lead to more backing-store access than is really necessary).

 * However, an overestimate will lead to failure.  Hence it's wise to subtract

 * a slop factor from the true available space.  5% should be enough.

 *

 * On machines with lots of virtual memory, any large constant may be returned.

 * Conversely, zero may be returned to always use the minimum amount of memory.

 */



EXTERN long jpeg_mem_available JPP((j_common_ptr cinfo,

				    long min_bytes_needed,

				    long max_bytes_needed,

				    long already_allocated));





/*

 * This structure holds whatever state is needed to access a single

 * backing-store object.  The read/write/close method pointers are called

 * by jmemmgr.c to manipulate the backing-store object; all other fields

 * are private to the system-dependent backing store routines.

 */



#define TEMP_NAME_LENGTH   64	/* max length of a temporary file's name */



#ifdef USE_MSDOS_MEMMGR		/* DOS-specific junk */



typedef unsigned short XMSH;	/* type of extended-memory handles */

typedef unsigned short EMSH;	/* type of expanded-memory handles */



typedef union {

  short file_handle;		/* DOS file handle if it's a temp file */

  XMSH xms_handle;		/* handle if it's a chunk of XMS */

  EMSH ems_handle;		/* handle if it's a chunk of EMS */

} handle_union;



#endif /* USE_MSDOS_MEMMGR */



typedef struct backing_store_struct * backing_store_ptr;



typedef struct backing_store_struct {

  /* Methods for reading/writing/closing this backing-store object */

  JMETHOD(void, read_backing_store, (j_common_ptr cinfo,

				     backing_store_ptr info,

				     void FAR * buffer_address,

				     long file_offset, long byte_count));

  JMETHOD(void, write_backing_store, (j_common_ptr cinfo,

				      backing_store_ptr info,

				      void FAR * buffer_address,

				      long file_offset, long byte_count));

  JMETHOD(void, close_backing_store, (j_common_ptr cinfo,

				      backing_store_ptr info));



  /* Private fields for system-dependent backing-store management */

#ifdef USE_MSDOS_MEMMGR

  /* For the MS-DOS manager (jmemdos.c), we need: */

  handle_union handle;		/* reference to backing-store storage object */

  char temp_name[TEMP_NAME_LENGTH]; /* name if it's a file */

#else

  /* For a typical implementation with temp files, we need: */

  FILE * temp_file;		/* stdio reference to temp file */

  char temp_name[TEMP_NAME_LENGTH]; /* name of temp file */

#endif

} backing_store_info;



/*

 * Initial opening of a backing-store object.  This must fill in the

 * read/write/close pointers in the object.  The read/write routines

 * may take an error exit if the specified maximum file size is exceeded.

 * (If jpeg_mem_available always returns a large value, this routine can

 * just take an error exit.)

 */



EXTERN void jpeg_open_backing_store JPP((j_common_ptr cinfo,

					 backing_store_ptr info,

					 long total_bytes_needed));





/*

 * These routines take care of any system-dependent initialization and

 * cleanup required.  jpeg_mem_init will be called before anything is

 * allocated (and, therefore, nothing in cinfo is of use except the error

 * manager pointer).  It should return a suitable default value for

 * max_memory_to_use; this may subsequently be overridden by the surrounding

 * application.  (Note that max_memory_to_use is only important if

 * jpeg_mem_available chooses to consult it ... no one else will.)

 * jpeg_mem_term may assume that all requested memory has been freed and that

 * all opened backing-store objects have been closed.

 */



EXTERN long jpeg_mem_init JPP((j_common_ptr cinfo));

EXTERN void jpeg_mem_term JPP((j_common_ptr cinfo));

